Closed loop automated matrix removal

ABSTRACT

An automated matrix removal module is configurable to automatically withdraw a portion of sample containing an interfering matrix. The module is further configurable to mix the portion of sample with a reagent selected to react with the matrix to form a precipitant and then filter the mixture of sample and precipitant reagent through a filter. Finally, the module is further configurable to flush the precipitant from the filter.

RELATED APPLICATION DATA

This application is a continuation-in-part of U.S. application Ser. No.10/641,946, filed Aug. 15, 2003, the contents of which are herebyincorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates generally to chemical analysis, and moreparticularly to apparatus for the removal of an interfering matrix priorto chemical analysis.

BACKGROUND

Automated systems for measuring the concentration of analytes in asample have been developed using a number of analytical techniques suchas mass spectrometry. For example, co-assigned U.S. application Ser. No.10/094,394, entitled “Automated In-Process Ratio Mass Spectrometry ForCharacterizing Constituents,” filed Mar. 8, 2002, the contents of whichare hereby incorporated by reference in their entirety, discloses anautomated in-process mass spectrometry (IPMS) apparatus for detecting,identifying, and quantifying chemical constituents and their reactionproducts in process solutions.

One type of process solution which an IPMS apparatus may analyze is acopper electroplating bath for the deposition of copper structures onsemiconductor wafers. The bath comprises a relatively concentratedacidic aqueous copper sulfate solution. Plating topology is controlledby organic plating solution additives within the copper sulfate solutionthat function to either suppress or accelerate the plating process.These additives experience electrochemical breakdown during the platingprocess and can be lost by drag out or by becoming trapped within theplated film. However, the achievement of void-free plating in the viasand trenches of sub-micron high-aspect-ratio structures requires verytight control of additive levels. Unlike indirect measurement methodssuch as cyclic voltametric stripping (CVS) that monitor theeffectiveness of the plating solution, the IPMS apparatus discussedabove allows a user to directly measure trace component concentration aswell as constituent concentration (including breakdown products) in theelectroplating bath to ensure a defect-free deposition process.

High sensitivity quantification of the organic additives and theirbreakdown by-products in the electroplating bath is hampered by therelatively high concentration of a matrix of sulfuric acid and coppersulfate within the bath. These relatively high concentrations ofprotons, sulfate, and copper ions obscure the detection andquantification of constituents such as organic additives becauseionization of the higher concentration ions is statistically more likelyin the ionization source of the mass spectrometer. Thus, the matrix ofcopper sulfate and sulfuric acid should be removed from the sample tomore accurately quantify the organic additive concentrations. Similarly,other metrology techniques such as flow injection analysis andchromatography often require the removal of chemical matrices that mayhamper the quantification of an analyte of interest. U.S. applicationSer. No. 10/641,946 discloses an automated matrix removal module inwhich a reagent is mixed with a sample having an interfering matrix sothat the matrix may be removed prior to quantification of the analyte(s)of interest. The reagent reacts with the matrix to form a precipitate,which is then removed using a filter.

The automated matrix removal module disclosed in U.S. application Ser.No. 10/641,946 advantageously includes a back-flush cycle to cleanse thefilter such that the module may remove matrix from samples continuallyfor periods of months. However, addition of an appropriate amount ofreagent depends upon the concentration of the interfering matrix. Forexample, in some instances it may be desirable to under-precipitate thematrix such that some matrix remains in the filtered sample.Alternatively, it may be desirable to “over-precipitate” the matrix suchthat some un-reacted reagent remains in the filtered sample. Attainingthe desired degree of precipitation can be difficult, however, becausethe concentration of the matrix may change. For example, with regard toa copper plating bath, both copper sulfate and sulfuric acid can beconsumed during a plating operation as well as being physically removedfrom the bath due to wafer removal. In addition, evaporation can occur,thereby changing copper sulfate and sulfuric acid concentrations.Moreover, replenishment of additives in the bath can also cause thematrix concentration to change if corresponding amounts of sulfuric acidand copper sulfate are not added simultaneously.

The potentially-dynamic nature of a matrix concentration thus makesmatrix removal problematic. For example, a matrix concentration may beassumed to be static such that a fixed amount of reagent is always addedto the sample within the automated matrix removal module. In such acase, the degree of precipitation will increase if the matrixconcentration decreases such as described earlier with regard to acopper plating bath. Over time, an undesired over-precipitation mayoccur. Alternatively, should the matrix concentration graduallyincrease, the degree of precipitation would gradually decrease until anundesired under-precipitation occurs.

Accordingly, there is a need in the art for automated systems for theremoval of interfering matrices prior to a chemical analysis whichdynamically respond to changes in concentration of the interferingmatrices.

SUMMARY

In accordance with the present invention, an apparatus for the automatedremoval of a matrix from a solution containing an analyte of interest isprovided. The apparatus includes: at least one analytical instrumentoperable to measure a concentration of the matrix in a sample of thesolution; a source of reagent, the reagent being reactive with thematrix to form a precipitate; a reaction vessel; and a filter, whereinthe apparatus has a filtering configuration in which a volume of thesolution and a volume of the reagent react in the reaction vessel toform a reaction mixture that is filtered through the filter, the volumeof the reagent being based upon the matrix concentration measurement,the apparatus having a flushing configuration in which the filter isback flushed with a solvent.

In accordance with another aspect of the invention, an apparatus isprovided that includes: a sample extraction module operable to extractsample from a selected one of a plurality of process solution baths; atleast one dilution and spiking module operable to spike and diluteextracted sample to form a processed solution; a source of reagentsolution reactive with a matrix in the processed solution to form aprecipitate; a plurality of matrix removal modules, each matrix removalmodule operable in a mixing cycle to mix the processed solution with thereagent solution to form a reaction mixture having the precipitate andto filter the precipitate from the reaction mixture through a filter toform a filtered solution, each matrix removal module operable in aflushing cycle to flush the filter; and

-   a control system to control the mixing and flushing cycles of the    plurality of matrix removal modules such that as one matrix removal    module is in the mixing cycle another matrix removal module is in    the flushing cycle.

In accordance with another aspect of the invention, an apparatus for theautomated removal of a matrix from a solution containing an analyte ofinterest is provided. The apparatus includes: at least one analyticalinstrument operable to periodically measure a concentration of thematrix; a source of reagent, the reagent being reactive with the matrixto neutralize the matrix; and a reaction vessel, wherein the apparatushas a neutralizing configuration in which a volume of the solution and avolume of the reagent react in the reaction to form a neutralizedmixture, the volume of the reagent being based upon a most-recent matrixconcentration measurement by the analytical instrument.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an automated matrix removal moduleaccording to an embodiment of the invention.

FIG. 2 is an illustration of an automated matrix removal moduleincluding a mixing tee according to an embodiment of the invention.

FIG. 3 is an illustration of an IPMS system incorporating a plurality ofclosed loop automated matrix removal modules.

Use of the same reference symbols in different figures indicates similaror identical items.

DETAILED DESCRIPTION

Reference will now be made in detail to one or more embodiments of theinvention. While the invention will be described with respect to theseembodiments, it should be understood that the invention is not limitedto any particular embodiment. On the contrary, the invention includesalternatives, modifications, and equivalents as may come within thespirit and scope of the appended claims. Furthermore, in the followingdescription, numerous specific details are set forth to provide athorough understanding of the invention. The invention may be practicedwithout some or all of these specific details. In other instances,well-known structures and principles of operation have not beendescribed in detail to avoid obscuring the invention.

FIG. 1 illustrates an exemplary automated matrix removal module 100.Module 100 includes a pump such as syringe pump 105. Syringe pump 105 isconnected to a conduit 110 when a three-way valve EV1 is properlyactuated. Three-way valve EV1 functions to connect syringe pump 105 toeither conduit 110 or to another three-way valve EV3. Conduit 110 isconnected to a source (not illustrated) of a sample solution containingan analyte which will be analyzed by a chemical analysis or metrologyinstrument (also not illustrated) after processing by module 100.Typical chemical metrology instruments include mass spectrometers,chromatography systems such as high performance liquid chromatography(HPLC), and flow injection analysis (FIA) systems. It will beappreciated, however, that the present invention is not limited by thetype of chemical metrology instrument used after processing by module100.

Regardless of the type of chemical metrology instrument that will beused to characterize the analyte of interest in the sample solution, theperformance of this instrument may be hampered by the presence of aninterfering chemical matrix. As used herein, “matrix” will be understoodto denote constituent(s) within the sample solution that hamper analysisof the analyte of interest by the chemical analysis or metrology tool.For example, as discussed earlier, copper sulfate and sulfuric acid actas chemical interferents in the characterization of organic additiveswithin a copper electroplating solution by a mass spectrometer. Thisinterference results from the hydrogen, copper, and sulfate ions beingpreferentially ionized within the mass spectrometer due to theirrelatively-high concentration, thereby obscuring the measurement of theorganic additive concentrations. The acid and copper sulfateinterferents may also be denoted as a “matrix” which must be removedbefore characterization of the organic additives. In general, a matrixmay comprise a plurality of chemical species.

To begin the process of removing the matrix from the sample solution,three-way valve EV1 is actuated so that as the plunger of syringe pump105 is withdrawn, a portion of the sample carried by conduit 110 isdrawn into syringe pump 105. Syringe pump 105 may be controlled by astepper motor (not illustrated) to precisely control the amount ofsample withdrawn into syringe pump 105. A reagent solution may then beadded to the contents of syringe pump 105 as follows. The appropriatereagent solution is provided by a reagent source 120 connected tothree-way valve EV3. The reagent is selected such that it will reactwith the matrix such that the matrix is no longer interfering. Forexample, the reagent-may react with the matrix to produce an insolubleprecipitant. In one embodiment, if the matrix is aqueous copper sulfateand sulfuric acid, a suitable reagent solution would be aqueous bariumhydroxide. With respect to the removal of copper sulfate and sulfuricacid from an aqueous solution using barium hydroxide, the reactionsoccur as follows:H₂SO₄+CuSO₄+2Ba(OH)₂→2H₂O+2BaSO₄+Cu(OH)₂Both BaSO₄ and Cu(OH)₂ are relatively insoluble in aqueous solutions andwould thus precipitate within the syringe pump. As another example, ifthe matrix comprises Ag⁺ ions in an aqueous sample, a suitable reagentmay comprise a source of Cl⁻ anions such as NaCl.

To mix the contents of syringe pump 105 with the reagent solution,three-way valves EV1 and EV3 are appropriately actuated to connectsyringe pump 105 to reagent source 120. The plunger of syringe pump 105may then be withdrawn to add the appropriate amount of reagent to thecontents of syringe pump 105. The appropriate amount of the reagentdepends upon the amount of matrix within the sample solution withdrawninto syringe pump 105. For example, each molecule of sulfuric acid andcopper sulfate in a copper plating bath sample requires the addition ofa corresponding molecule of barium hydroxide for a perfect removal andneutralization of the matrix. However, as discussed earlier, theanalysis following matrix elimination may be better performed if thematrix is “under-precipitated” such that some matrix remains despite theaddition of the reagent. Alternatively, the analysis following matrixelimination may be more accurate if the matrix is “over-precipitated”such that the matrix is eliminated yet un-reacted reagent remains.

To provide the appropriate amount of reagent, the concentration of thematrix may be assumed to be static such that a fixed volume of reagentsolution may be added based upon the volume of sample solution needingmatrix elimination. Alternatively, the matrix concentration may bemeasured periodically such that the volume of reagent solution beingadded depends upon the latest measured matrix concentration. Forexample, it has been shown that the copper sulfate concentration andsulfuric acid concentration in copper electroplating bath solution hasappreciable variability in semiconductor manufacturing operations. Thus,an addition of a fixed volume of Ba(OH)₂ solution to samples of copperelectroplating solutions may result in either under-precipitation orover-precipitation of the copper sulfate/sulfuric acid concentrations.In general, an addition of a variable volume of reagent solution basedupon periodic measurements of the concentrations of the matrix avoidssuch over-precipitation or under-precipitation problems. Suchembodiments may be denoted as “closed loop” embodiments in that feedbackinformation (the latest measurement of the matrix concentration to beeliminated) is used to update the amount of reagent being added. Incontrast, embodiments in which the amount of reagent being added isstatic may be denoted as “open loop” embodiments in that no feedbackinformation is utilized.

Regardless of whether a fixed volume or variable volume of reagentsolution is used, the flow of reagent solution into syringe pump 105 maybe aided by pressuring reagent solution source 120 with an inert gassuch as nitrogen. Alternatively, a mechanical pump may be used to assistthe flow of reagent solution into three-way valve EV3.

After the addition of reagent solution into syringe pump 105, additionalsolvent may be optionally added to flush the three-way valves of reagentsolution. For example, in the case of removing a copper sulfate andsulfuric acid matrix as discussed above, the additional solvent may beultra pure water (UPW). In the exemplary embodiment for module 100 shownin FIG. 1, this additional solvent is supplied by a source 130 connectedto conduit 125 that in turn connects to three-way valve EV5. Byappropriate actuation of three-way valves EV1, EV3, and EV5, source 130is connected to syringe pump 105 such that as the plunger of syringepump 105 is withdrawn, a predetermined amount of solvent may be added tothe contents of syringe pump 105. Source 130 may also be pressurizedwith an inert gas such as nitrogen to aid in the injection of solventinto three-way valve EV5. After any addition of solvent to syringe pump105, the contents of syringe pump 105 may be further processed by, forexample, heating, cooling, or by simply waiting to aid in the formationof precipitate as required. With respect to precipitation of Cu(OH)₂ andBaSO₄ as discussed above, no heating or cooling of syringe pump 105 isnecessary.

Although no cooling or heating of syringe pump 105 is necessary, themixture of sample solution and reagent solution within syringe pump 105benefits from physical mixing to assist the desired reaction between thetwo solutions. For example, syringe pump 105 may include a side port 149that is exposed after the plunger is withdrawn. In general, thisexposure will occur after the mixture of sample solution and reagentsolution has been added to syringe pump 105. Valve EV2 to a drain port170 is opened and the plunger for syringe 105 is withdrawn until thevalves EV1, EV3, and EV5 are cleared of solution. To ensure ahomogeneous mixture, valve EV2 to drain port 170 can be left open whilethe plunger for syringe 105 is withdrawn until side port 149 isconnected. Once side port 149 is fluidly connected to drain 170, aninert gas such as N₂ may flow through a conduit 151 and a three-wayvalve 152 and bubble through the contents of syringe pump 105 and outport 170 for a period of time. Advantageously, such bubbling mixes thecontents of syringe pump 105 without requiring any physical movement oragitation of syringe pump 105. In this fashion, stress-induced fracturesor strain of the various conduits attaching to syringe pump 105 fromphysical agitation are avoided as well as the cost of an agitatingcomponent.

After adequate mixture of the contents of syringe pump 105, thecompletion of desired precipitation reactions within syringe pump 105may be assumed. At this point, syringe pump 105 may pump its contentsthrough a filter 140. However, to avoid clogging filter 140 with thefull amount of the resulting precipitate, the contents of syringe pump105 may be allowed to settle. For example, syringe pump 105 may beoriented such that gravity pulls the precipitate towards side port 149.If the plunger of syringe pump 105 is then just partially actuated suchthat the bulk of the precipitate remains in syringe pump 105, the lifeof filter 140 is extended. Alternatively, all the contents of syringepump 105 may be filtered. Before syringe pump 105 may pump its contentsthrough filter 140, three-way valves EV1, EV3, EV5, EV2, and EV4 areappropriately actuated to connect syringe pump 105 to filter 140. Thepore size for filter 140 is chosen appropriately as determined by theflow rate, solvent, and expected type of precipitate that will befiltered by filter 140. For example, to filter the Cu(OH)₂ and BaSO₄precipitants discussed previously, a suitable pore size for filter 140is approximately 0.45 um. By proper actuation of three-way valve EV6,the filtered contents pass through filter 140 into conduit 145 foreventual processing by a chemical analysis or metrology instrument (notillustrated).

Although filter 140 will have thus removed any solid precipitate in thefiltered solution provided to the chemical metrology instrument,unfiltered solution and precipitate will now be contaminating module100. Thus, module 100 may be flushed as follows before another cycle ofreceiving a sample, mixing the sample with a reagent, and filtering themixed solution may begin. To begin the flush cycle, the plunger ofsyringe pump 105 is withdrawn a sufficient amount to expose back flushport 149. With back flush port 149 exposed, three-way valves EV5, EV3,EV1, and 152 are appropriately actuated so that solvent source 130 isconnected through syringe pump 105 to a drain 155. Because solventsource 130 may be pressurized, solvent will then flush from solventsource 130 through back flush port 149 into drain 155. Alternatively, amechanical pump may be used to force solvent into three-way valve EV5and eventually to drain 155.

While syringe pump 105 is flushed, filter 140 may also be back-flushed.To back-flush filter 140, three-way valves EV6, EV4, and a three-wayvalve 162 are appropriately actuated to connect a solvent source 160 ora solvent source 161 to a drain 165. An inert gas such as nitrogen maybe used to pressurize solvent source 160 such that solvent will thenflow through three-way valve EV6, and through filter 140 and three-wayvalve EV4 into drain 165, thereby back-flushing filter 140 of theprecipitate from the previous filtering cycle. Solvent sources 161 and162 may comprise different solvents such as ultra pure water or dilutenitric acid. The life of filter 140 may be substantially extended inthis fashion.

An additional back flush of filter 140 may be performed by appropriatelyactuating three-way valves EV1, EV3, EV5, EV2, EV4, EV4, EV6, and 162 toconnect the remaining one of solvent source 160 or 161 to syringe pump105. Syringe pump 105 is withdrawn to the side port 149 wherebythree-way valve 152 is appropriately actuated to connect the backflushport 149 to drain 155. Solvents 160 or 161 are then allowed to flow todrain 155 for a predetermined amount of time. After the predeterminedflushing time, the three-way valves are actuated to their default,normally open state.

To complete the flushing cycle, three-way valves EV1, EV3, EV5, and EV2are appropriately actuated to connect syringe pump 105 to a drain 170.The plunger of syringe pump 105 is then depressed. Because syringe pump105 will have been filled with clean solvent after sufficient flushingthrough back flush port 149, clean solvent will then flush throughthree-way valve EV2 into drain 170, thereby flushing three-way valveEV2. It will be appreciated that the presence of drain 170 is a resultof the use of three-way valves—three-way valve EV4 cannot be actuated soas to connect drain 165 to syringe pump 105. Thus, after flushingsyringe pump 105, its contents must be emptied into another drain suchas drain 170. In alternative embodiments that do not use three-wayvalves, this extra drain would be unnecessary. For example, one or moretwo-position multi-way valves such as rotary valves could be employed toalternatively connect syringe pump 105 to the sample source, to thereagent source 120, to filter 140, and finally to a drain.

Consider the advantages provided by module 100. Because the variouscomponents may all be actuated according to commands from amicroprocessor or state machine, the operation is entirely automated andrequires no human intervention. Moreover, because of the flush cycle,filter 140 may be reused for many cycles, thereby keeping operationcosts low. However, the time required to (if desired) mix the contentsof syringe pump 105 to ensure completion of desired precipitationreactions, allow the contents to settle, and flush syringe pump 105 maybe problematic.

Such delay is avoided in an alternative automated matrix removal module200 as illustrated in FIG. 2. Sample solution and reagent solution enteropposite arms of a mixing tee 205. Thus, the solutions turbulently mixtogether within mixing tee 205 such that no physical agitation isnecessary to ensure that the desired reactions have been completed.Whereas the body of syringe pump 105 forms the reaction vessel in whichmatrix elimination reactions occur for module 100, the reaction vesselfor automated matrix removal module 200 is mixing tee 205 and its theexit conduit 210. Thus, the flow rates of the sample solution andreagent solution into mixing tee 205 should be carefully controlled toensure that a desired stoichiometry for the matrix elimination reactionis achieved. In this fashion, under-precipitation or over-precipitationof the matrix within the sample solution is avoided through control ofthe flow rates into mixing tee 205. If an analyte is better analyzed inan under-precipitated or over-precipitated solution, flow rates may beadjusted accordingly to achieve the desired result.

It will be appreciated that numerous pumping configurations may be usedto effect the desired flow rates into mixing tee 205. For example, afirst syringe pump 220 may withdraw a desired volume of the samplesolution from a sample source 225 through appropriate actuation of athree-way valve 230. After three-way valve 230 is appropriately actuatedso that syringe pump 220 is connected to mixing tee 205, syringe pump220 may force its contents into mixing tee 205. Similarly, a syringepump 240 may withdraw a desired volume of reagent solution from areagent solution source 245 through appropriate actuation of a three-wayvalve 250. After three-way valve 250 is appropriately actuated so thatsyringe pump 240 is connected to mixing tee 205, syringe pump 240 maypump its contents into mixing tee 205 simultaneously with the flow ofsample solution pumped from syringe pump 220. The resulting mixture frommixing tee 205 flows through conduit 210 into filter 140 as forced bythe actuation of syringe pumps 220 and 240. Filter 140 may then beback-flushed with solvent from sources 160 and 161 through appropriateactuation of three-way valves EV4, EV6, and 162 as discussed with regardto FIG. 1.

Multiple automated matrix elimination modules such as module 100 or 200may be employed in a chemical analysis or metrology system. For example,automated matrix elimination modules may be advantageously incorporatedinto an IPMS system used to analyze the concentrations of constituentsin copper electroplating baths. Turning now to FIG. 3, an IPMS system300 includes a sample extraction module 305 adapted to withdraw samplesolutions from a plurality of baths 310. Sample extraction module (SEM)305 may be configured as discussed in co-assigned U.S. application Ser.No. 10/094,394. For example, SEM 305 may include a syringe pump (notillustrated) that withdraws an appropriate amount of sample solutionfrom a selected bath 310 as determined through a selection valve (notillustrated). Samples extracted by SEM 305 are processed throughdilution and spike modules 360 and 365. Each module 360 and 365 may beimplemented as described, for example, in U.S. application Ser. No.10/641,480, entitled “Loop Dilution System,” filed Aug. 15, 2003, thecontents of which are incorporated by reference herein. In a loopdilution implementation, dilution and spike modules 360 and 365 wouldinclude one or more multi-way valves (not illustrated) connected to dualtubings or conduits (the loops). To perform the spiking, a first loop isfilled with sample and a second loop filled with spike solution. Thenature of the spike depends upon the analyte being analyzed in thesample. For example, to determine the concentrations of bis(3-sulfopropyl) disulfide (SPS) in a selected copper electroplating bathusing IPMS system 300, modules 360 and 365 may spike the sample from SEM305 with a known amount of bis (3-sulfoethyl) disulfide (SES). SES issufficiently similar to SPS in molecular weight and chemical behaviorsuch that it acts a chemical homologue to SPS upon ionization andcharacterization within a mass spectrometer (not illustrated) in IPMSsystem 300. Thus, by performing a ratio measurement using a resultingspectrum from the mass spectrometer, IPMS system 300 may determine theconcentration of SPS in the selected electroplating bath solution basedupon the known concentration and volume of SES added in modules 360 and365. In general, multiple spikes may be added to a sample, wherein thespikes correspond to multiple analytes.

Regardless of how many spikes are added, the multi-way valve is thenactuated such that the loops are connected with a diluent source (suchas a syringe pump filled with diluent) which may then mix the contentsof the connected loops with the diluent. Should additional dilution berequired, the diluted and spiked sample may then be processed inadditional dual-loop multi-way valves. In these additional valves, oneof the loops is filled with diluent rather than spike, since spiking hasalready taken place. The remaining loop is filled with diluted andspiked sample from the previous multi-way valve. It will be appreciatedthat a single spike and dilution module may be used rather than multiplemodules 360 and 365. However, by using two or more of such modules, adiluted and spiked sample may be delivered by one of the modules whileanother is still performing its dilution and spiking operations, therebyenhancing throughput.

Through appropriate actuation of either selection valve 330 or selectionvalve 370, processed sample from modules 360 and 365 may have its matrixeliminated in a selected one of a plurality of matrix eliminationmodules 340. Each of the matrix elimination modules 340 may beimplemented such as described with regard to modules 100 and 200. Itwill be appreciated that just a single matrix elimination module 340could be used in IPMS system 300. However, by providing a plurality ofmodules 340, each module may be specialized to the analysis of a givenanalyte. For example, a first module 340a may be dedicated to theanalysis of SPS. Such analyses are best performed such that the matrixis under-precipitated, leaving the treated solution slightly acidic. Incontrast, the analysis of polyethylene glycol (PEG) is best performedsuch that the matrix is over-precipitated, leaving the treated solutionslightly basic. Thus, a second module 340 b may be dedicated to theanalysis of polyethylene glycol (PEG), and so on. In addition, theprovision of a plurality of modules 340 allows for pipelining such thatas one module is performing a back flush or otherwise getting preparedfor another cycle of matrix elimination, another module is activelyeliminating its matrix, and so on.

The following discussion will assume that IPMS system is analyzing baths310 of a copper plating solution as an exemplary embodiment. Asdiscussed earlier, an open loop addition of reagent solution such as aBa(OH)₂ solution by modules 340 may be problematic in that matrixconcentration (such as copper sulfate and sulfuric acid in the copperelectroplating solutions) is often variable and thus dependent uponsampling time. To allow for closed loop control of the addition ofreagent solution, IPMS system 300 includes one or more analyticalinstruments. For example, IPMS system may monitor the copper sulfate andsulfuric acid concentrations in baths 310 using an optical spectroscopymodule 350 and a pH ion selective electrode 355. In an alternativeembodiment, the mass spectrometer in IPMS system 300 may itself serve asthe analytical instrument that monitors the matrix concentration. Thelocation of the analytical instruments may thus be “in-line” in thatthey are located in a sample path connecting to the mass spectrometer.Alternatively, they may be located “off line” in a sample path that doesnot connect to the mass spectrometer. In the embodiment illustrated inFIG. 3, optical spectroscopy module 350 is located off line. In thatregard, samples provided to module 350 by SEM 305 need no spiking.However, such samples may need to be diluted for optimal performance ofmodule 350. Thus, samples provided to optical spectroscopy module 350may be diluted in a sample dilution module 320. Sample dilution module320 may be implemented using a loop dilution technique as discussed withregard to modules 360 and 365. However, because no spiking occurs inmodule 320, diluent fills one of the loops rather than spike solution.

As known in the optical absorption arts, optical spectroscopy module 350may include a liquid flow cell coupled to an optical spectrometer. Alight source shines light through the liquid flow cell into the opticalspectrometer so that a measurement of the optical transmittance throughthe diluted sample may be conducted. Periodically, optical spectroscopymodule 350 may be recalibrated by determining the absorption of a blanksolution (such as UPW) and a control solution of copper sulfate having aknown concentration.

The optical transmittance of the diluted sample is related tomeasurements by the optical spectrometer. For example, a UV/VISspectrometer may read units of “counts,” where each count is equivalentto a number of photons (for example, 100 photons) impacting a CCDdetector within the spectrometer. Thus, a blank count would correspondto counts measured by the UV/VIS spectrometer when the blank solution(such as UPW) is flowing through the illuminated liquid flow cell. Incontrast, a dark count would correspond to counts measured when no lightis transmitted into the liquid flow cell. A sample count wouldcorrespond to the counts measured by the UV/VIS spectrometer when sampleis flowing through the illuminated liquid flow cell. Given thesedefinitions, the transmittance of a sample corresponds to the ratio:(sample count-(blank count-dark count)/(blank count-dark count).

Given the transmittance, the concentration of copper (and thus coppersulfate) may be determined through application of Beer's law:A=εbcwhere A is absorbance, E is emissivity coefficient, b is the opticalpath length in the liquid flow cell, and c is concentration. In turn,the absorbance is related to the transmittance as:A=−log(transmittance)

Standard techniques to achieve optical instrument stability can be used.For example light from a source can be split with one beam passingthrough the flow cell to a detector to provide a signal. A second beamis directed at a detector to provide a reference signal thereby allowingcorrections to be made for varying light source intensity. In oneexample, a preferred range of copper concentration for optimalperformance of optical spectroscopy module 350 is between 0.5 g/L and 5g/L of copper. If the concentration of copper in the copperelectroplating bath solutions is approximately 40 g/L, sample dilutionmodule 320 should dilute the samples for optical analysis by a factor ofapproximately 20:1.

Ion selective electrode 355 may be located inline or offline asdiscussed with regard to optical spectroscopy module 350. To receive asample at ion selective electrode 355, selection valve 330 and athree-way valve EV16 are actuated accordingly. It will be appreciatedthat the mass spectrometer itself may comprise the analytical instrumentthat measures the matrix concentration. In general, however, it will notbe the mass spectrometer (or whatever type of chemical metrologyinstrument being implemented) if the matrix is problematic to thatinstrument.

As discussed analogously in U.S. application Ser. No. 10/094,394, IPMSsystem 300 includes one or more processors (not illustrated) thatcontrol the automated analysis of analytes of interest in the sampledsolutions by the remaining components in IPMS system 300. Thus, aprocessor may be configured to determine the amount of Ba(OH)₂ addedwithin modules 340 from measurements by optical spectroscopy module 350and the analyte pH using ion selective electrode 355 as follows. Fromthe copper concentration of a sampled bath solution (in grams/L)determined by the optical absorption measurements in opticalspectroscopy module 350 (with consideration of the dilution as well),the moles/liter of Cu in the undiluted sample is given by (concentrationin grams/L)/(molecular weight of Cu). Similarly, the measured pH fromion selective electrode 355 may be used to determine the concentrationof sulfuric acid in grams/L in the undiluted sample. In turn, theconcentration of sulfuric acid may then be divided by the molecularweight of sulfuric acid to obtain the concentration of sulfuric acid inmoles/L. The concentration of sulfate in the sampled bath (in moles/L)is thus given by the sum of the ((moles of Cu)/L) and the ((moles ofsulfuric acid)/L) concentrations.

Given the concentration of sulfate in the sampled bath, theconcentration of sulfate in the diluted bath sample from sample dilutionmodule 320 will depend upon the dilution ratio being implemented. Foreach mole in the diluted sample, a corresponding mole of Ba(OH)₂ may beadded in matrix elimination modules 340. However, a factor may be eithersubtracted from the calculated moles of Ba(OH)₂ or added to preciselyobtain the desired pH level. For example, referring again to FIG. 1,syringe pump 105 would be actuated to add an appropriate volume ofBa(OH)₂ based upon the concentration of source 120 to provide thedesired moles of Ba(OH)₂ as given by the most recent measurement of thesulfate concentration. The frequency of measurements by opticalspectroscopy module 350 and pH ion selective electrode 355 depend uponthe expected variability of the matrix concentration in the copperelectroplating baths.

The above-described embodiments of the present invention are merelymeant to be illustrative and not limiting. For example, there may beembodiments in which a matrix need not be precipitated but merelyneutralized. For example, if the matrix comprises sulfuric acid but themetrology instrument is only affected by the acidity, the sulfuric acidmay be neutralized by an appropriate addition of a reagent such as NaOH.In such an embodiment, the filter would be unnecessary. Moreover,dilution module 100 of FIG. 1 may be modified by replacing syringe pump105 with another type of pump. In addition, the three-way valves may bereplaced by other valve means. It will thus be obvious to those skilledin the art that various changes and modifications may be made withoutdeparting from this invention in its broader aspects. Accordingly, theappended claims encompass all such changes and modifications as fallwithin the true spirit and scope of this invention.

1. An apparatus for the automated removal of a matrix from a solution containing an analyte of interest, comprising: at least one analytical instrument operable to measure a concentration of the matrix in a sample of the solution; a source of reagent, the reagent being reactive with the matrix to form a precipitate; a reaction vessel; and a filter, wherein the apparatus has a filtering configuration in which a volume of the solution and a volume of the reagent react in the reaction vessel to form a reaction mixture that is filtered through the filter, the volume of the reagent being based upon the matrix concentration measurement, the apparatus having a flushing configuration in which the filter is back flushed with a solvent.
 2. The apparatus of claim 1, wherein the reaction vessel comprises a syringe pump.
 3. The apparatus of claim 1, wherein the reaction vessel is a mixing tee.
 4. The apparatus of claim 2, wherein the syringe pump includes a side port, and wherein the apparatus is configured in the flushing configuration such that the contents of the syringe pump are flushed into the side port.
 5. The apparatus of claim 4, further comprising a source of inert gas configurable to pump the inert gas into the side port if the apparatus is in the mixing configuration such that the inert gas bubbles through the reaction mixture.
 6. The analytical apparatus of claim 2, wherein the apparatus is configured in the filtering configuration such that the syringe pump may pump solvent into a body of syringe pump to mix with the reaction mixture.
 7. The analytical apparatus of claim 1, wherein the apparatus is responsive to electronic commands for controlling whether the apparatus is in the mixing or flushing configuration.
 8. The analytical apparatus of claim 1, wherein the at least one analytical instrument comprises an optical spectroscopy module.
 9. The analytical apparatus of claim 8, wherein the at least one analytical instrument further comprises an ion selective electrode.
 10. The analytical apparatus of claim 1, wherein the reagent source is a source of aqueous barium hydroxide.
 11. The analytical apparatus of claim 10, wherein the matrix comprises copper sulfate and sulfuric acid.
 12. The analytical apparatus of claim 1, further comprising a chemical metrology instrument for analyzing the reaction mixture filtered through the filter.
 13. The analytical apparatus of claim 1, wherein the chemical metrology instrument is a mass spectrometer.
 14. An apparatus, comprising: a sample extraction module operable to extract sample from a selected one of a plurality of process solution baths; at least one dilution and spiking module operable to spike and dilute extracted sample to form a processed solution; a source of reagent solution reactive with a matrix in the processed solution to form a precipitate; a plurality of matrix removal modules, each matrix removal module operable in a mixing cycle to mix the processed solution with the reagent solution to form a reaction mixture having the precipitate and to filter the precipitate from the reaction mixture through a filter to form a filtered solution, each matrix removal module operable in a flushing cycle to flush the filter; and a control system to control the mixing and flushing cycles of the plurality of matrix removal modules such that as one matrix removal module is in the mixing cycle another matrix removal module is in the flushing cycle.
 15. The apparatus of claim 14, further comprising: a mass spectrometer operable to process the filtered solution from each matrix removal module to form a ratio response, wherein the control system is further operable to measure the amount of at least one analyte based upon the ratio response.
 16. The apparatus of claim 15, further comprising: at least one analytical instrument operable to measure a concentration of the matrix, wherein the control system controls each matrix removal module in the mixing cycle to mix the processed solution with a volume of reagent solution based upon the measured concentration from the analytical instrument.
 17. An apparatus for the automated removal of a matrix from a solution containing an analyte of interest, comprising: at least one analytical instrument operable to periodically measure a concentration of the matrix; a source of reagent, the reagent being reactive with the matrix to neutralize the matrix; and a reaction vessel, wherein the apparatus has a neutralizing configuration in which a volume of the solution and a volume of the reagent react in the reaction to form a neutralized mixture, the volume of the reagent being based upon a most-recent matrix concentration measurement by the analytical instrument.
 18. The apparatus of claim 17, further comprising: a chemical metrology instrument operable to analyze a concentration of at least one analyte in the neutralized mixture.
 19. The apparatus of claim 17, wherein the analytical instrument comprises an optical spectrometer.
 20. The apparatus of claim 17, wherein the analytical instrument comprises a mass spectrometer. 